The cilia-associated respiratory (CAR) bacillus was first demonstrated with silver stains of sections of the respiratory tract of rats by workers in the Netherlands. It was isolated in embryonated hens' eggs by the staff of the Comparative Pathology Section and is believed to be a member of the group of gliding bacteria. The Bacillus has been associated with chronic respiratory disease in rats and mice. Peribronchial lymphoid infiltrates and hyperplasia of the mucosa associated lymphoid tissue were present in rabbits naturally infected with CAR bacillus. Experimental infection via the intranasal route resulted in CAR bacillus colonization of the nasal passages but no pulmonary pathology. This suggests that CAR bacillus is a minor respiratory pathogen in rabbits.